Previous work in LMB has led the way towards the ambitious goal where stem cells can be used to replace tissue damaged by neuro-degenerative diseases that cause the loss of neurons or glial cells. Our previous studies showed that large numbers of functional dopamine neurons can be derived from mouse and human embryonic stem cells. This is the type of neurons lost in Parkinson?s patients, a disease that afflicts more than one million Americans. However the clinical potential of stem cells might be exploited in two ways: cell therapy uses their ability to self-renew and differentiate in vitro prior to transplantation but clinical benefit might also be obtained by stimulating endogenous stem cells found in adult tissues (the ?if you have them ? use them? approach). Boosting endogenous stem cells will overcome the difficulty of immune rejection and may lead to simple pharmacological strategies to slow or reverse disease. In the past year we have made significant progress towards (1) establishing routine in vitro systems to study signaling pathways in human neurons and (2) developing new strategies for Parkinson?s disease and ischemia that target endogenous repair systems. [unreadable] [unreadable] Based on our experience placing fetal neural stem cells in tissue culture we have developed protocols that (1) allow the infectivity of Prions to be assessed more accurately and (2) allow human neurons to be derived from embryonic stem cells and from adult tissue. This work will provide model systems to asses the functional significance of mutations causing psychiatric and neurodegenerative disease in human neurons.[unreadable] [unreadable] Following our demonstration of widespread regeneration in the ischemic adult brain, we are now pursuing two specific goals. First we have identified cells in the parenchyma of the brain with stem cell properties. These cells raise the exciting possibility that general growth mechanisms, used during development can promote regeneration by boosting the patient?s own repair mechanisms incells that are proximal to the site of injury or disease. Second, we have identified of dopamine precursors as floor plate cells and shown that genes regulating floor plate development control dopamine neuron numbers in the laboratory. The production of midbrain dopamine neurons in the laboratory is a leading example of the potential of stem cell based therapies in medicine. The forkhead factor, foxa2, is expressed in the floor plate and required for the development of dopamine neurons but not for neurons derived from more lateral precursors outside of the floor plate. Foxa2 continues to be expressed in adult dopamine neurons and mice carrying only one copy of this gene show asymmetric behavioral abnormalities as they age. These mice show a corresponding late-onset asymmetric deficit in substantia nigra neurons while cells in the ventral tegmental area are less affected. These results suggest that targeting the survival function of the foxa2 forkhead gene will allow powerful new approaches to stem cell based and pharmacological approaches to dopamine neuron disease.